New stem cell reservoir found in blood

Freshly isolated monocytes in (a), with the other three images taken five days later, b) representing untreated monocytes, and d) is the culture that has been treated by the epidermal growth factor (Pic: PNAS)

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A new type of stem cell in white blood cells has been discovered by U.S. researchers, opening up potential alternatives to embryonic stem cells for treatment of transplant patients.

Adult stem cells are known to lurk in the marrow of bones where blood is made. In this latest work, Dr Eliezer Huberman, a molecular biologist at the Argonne National Laboratory in Chicago, tried to identify blood cells that might be able to act like stem cells.

They studied adult monocytes, a type of white blood cell. Using a series of growth factors, they were able to make the monocytes convert into a range of different types: epithelial cells, neuronal cells, liver cells, T lymphocytes and mature macrophages. The results appear in this week's Proceedings of the National Academy of Sciences.

"The research provides more evidence for a cell in bone marrow that can differentiate into a whole lot of different cell types," said Professor Perry Bartlett, a molecular neuroscientist at Brisbane's University of Queensland.

But more evidence is needed, he said, because these results are based on morphology - what the cells look like - and does not show definitely that the cells are fully differentiated. There is no evidence for the cell's functionality or physiology, he said.

Adult vs embryonic stem cells

The finding strengthens the argument that adult stem cells - as opposed to those extracted from embryos - are able to form many different types of cells too. The reasoning behind using embryonic stem cells is they are more 'plastic' than adult stem cells and have the potential to change into a wider range of cells.

"That's not really true," Bartlett told ABC Science Online. "This population has the potential to turn into large numbers of cell types."

While this is the first time monocytes have been identified as stem cells, blood has been shown to be a source of stem cells before. In July last year, researchers announced the first discovery of mesenchymal stem cells in blood. "This appears to be a different population of cells, derived from monocytes rather than mesenchymal cells," said Bartlett.

Monocytes are found in the lymphatic and circulatory systems where their purpose is to remove foreign particles, such as bacteria and tissue debris, by ingesting them. Because monocytes can be easily gathered from a patient's own blood supply, the researchers suggest that monocytes may be valuable candidates for transplantation therapies.

It may mean that rather than having transplants, patients may be able to repair liver or skin damage using cells cultured from their own blood, added Bartlett.

"The blood is synergetic," he said. "It is identical to the patient's. If the stem cells can grow up into epithelial cells, then instead of replacing the skin in burns patients, it can be replaced with the patient's own cells."